Muffler



Nov. 23, 1937. l.. R. HEATH 2,099,887

MUFFLER Filed May 26, 1934 2 Sheets-Sheet l ./mf @gm I l V MPL@ Nov. 23, 1937. L, R HEATH 2,099,887

MUFFLER Filed May 2e, 19:54

2 Sheets-Sheet 2 MMf/zmw Patented Nov. 23, 1937 UNITED STATES PATENT OFFICE MUFFLEB,

Laurence R. Heath, Buffalo,

N. Y., Signor to Application May 26, 1934, Serial No. 727,649

7 claims.

improvements in use in connection with This invention relates to muiliers or silencers for silencing the noises of the exhaust of internal combustion engines.

The objects of this invention are to provide a through type or low pressure muiiier of simple design which attenuates the power impulses or resonant sound waves; also to provide within a muflier resonator chambers having fundamental frequencies corresponding to the fundamental resonance frequency and related harmonics of the tail pipe leading from the muiiler to the air; also to provide a mufiier which includes outer resonating chambers which are connected by means of constricted 'passages or necks to inner chambers communicating through a series of small openings or perforations with a conduit or passage for exhaust gases; also to provide a muffler of this type in which the resonator chamber and neck is so proportioned as to eliminate sounds caused by the resonance of the tail pipe leading from the discharge end of the muiiler to the air; also to provide a muffler in which the ends of the intermediate shell form necks with an imperforate portion of the main gas conduit through the muiiier communicating with a resonance chamber; also to provide a muiller of this kind in which an end portion of the intermediate shell is supported on the main conduit by longitudinal spacing members which also form a plurality of separate neck portions communieating with a resonator chamber; also to provide a muffler of this type in which a perforated baffle is interposed between the resonance chamber and the neck portion of the mulller; also to improve the construction of muiilers of this kind in other respects hereinafter specied.

In the accompanying drawings:

Fig. 1 is a side view of a muilier embodying this invention and connected with an exhaust and a tail pipe.

Fig. 2 is a longitudinal central sectional elevation of the muilier.

Fig. 3 is a transverse sectional view thereof, on line 3 3, Fig. 2.

Figs. 4 and 5 are longitudinal central sectional views of muillers of modified construction.

Fig. 6 is a transverse section of the muiller shown in Flg. 5 on lines 6 6, Fig. 5.

Fig. 7 is a longitudinal central sectional view of a muiiler of another modified form.

Figs. 8 and 9 are transverse sections thereof on lines 8 8 and 9 9, Fig. 7.

Referring to Fig. 1, A represents the muiller to which an exhaust pipe B leading from the (ci. 1x1-4s) engine is connected and C represents the usual tail pipe leading from the discharge end of the muiiier to the rear of the vehicle on which the mumer is used.

I have found that in the design of mulilers of the type having sound absorbing or resonating chambers, the length of the tail pipe C has an important bearing upon the silencing action of the muliler. It has been found, for example that a muiller which effectively silences the noise of the exhaust of a certain type of engine when used in connection with a tail pipe of a certain length, will be noisy when used with a tail pipe of different length. I have found that while a long tail pipe is effective in reducing a certain noise called blatt, such tail pipe, nevertheless, resonates at both odd and even harmonics and has two distinct fundamental frequencies as a result of being only partially closed at the muilier end.

For example, a well known eight cylinder aun tomobile has resonance periods at 10%, 16, 2li/3, 26% and 32 miles per hour. The engine of this automobile makes 3231 revolutions per mile and the tail pipe leading from the muiiler is six feet long. This gives engine impulse frequencies of 38, 57, 76, and 114 per second respectively at these various speeds. The tail pipe fundamental resonance frequencies are per second corresponding to resonance periods at 32 'and 16 miles per hour, the velocity of sound in hot exhaust gases being approximately 1368 feet per second. The other resonance periods were not as loud as those at 16 and 32 miles per hour, but it will be noted that they have harmonic relation so that any attenuation of the 16 or 32 miles per hour periods will likewise attenuate the other periods, as well as their higher harmonics.

From the foregoing,

' change in the tail it will be realized that any pipe length changes its resonance. Filters designed to attenuate very broad bands of sound to accommodate any length of tail pipe are not efilcient from a silencing standpoint unless they comprise aplurality of units, or are of a size beyond that practical for average installations.

In muiliers embodying this invention, I have d limited the main filters to two, of which at least one is similar to the Helmholtz neck type resonator. Such resonators can be made with resonance bands broad enough to eliminate the sound due in which to the resonance of the tail pipe and are very eincient otherwise.- In some cases, one resonator is tuned to the frequency and the other to C N 2L in which N is fundamental frequency to be attenuated, c" the velocity of sound in the medium and L the length of the tail pipe. In other cases, I may tune these resonating chambers to C Nrn and E. L in which N2 is the half harmonic of N. I do not limit my invention to any particular combination of resonators, except that they must either have resonance frequencies the same as the iundamental frequencies or harmonic frequencies of the tail pipe.

I have found that by substituting the-proper values in the following equations, approximate values may be obtained for the unknown quantities. Corrections should be then undertaken, always bearing in mind that any increase in the dimensions of the cavity, any increase in the length jof the neck of the resonator, or any decrease in the area of the neck will lower the resonators fundamental frequency. The formula which I have devised is as follows:v

' 4 =area of perforation in conduit communieating with the neck, divided by the crosssectional area of the conduit e=velocity of sound in the medium s=area of resonator neck lzlength oi resonator neck v=volume of resonator cavity llt=radius of resonator neck R1=radius of resonator cavity L1=length of resonator cavity N=frequency to be attenuated.

The area or those slots or periorations in the conduit which communicate with the neck should not exceed the cross-sectional area of the conduit and the cross-sectional area of the resonator neck should be about equal to the cross-sectional area of the conduit.

In order to construct a muiiier incorporating the principles outlined, and to which the foregoing formulae are applicable, a number of muillers are illustrated in the drawings merely by way of examples, it being understood that my invention may be embodied in murders of other constructions than those shown. In all of these muiilers a central straight through passage or conduit is employed which has a relatively large number of perforations-therein, an intermediate shell surrounding the inner conduit and connected therewith by means of one or more bafiies, thus forming sound impedance chambers. 'Ihe intermediate shell is surrounded by an outer shell 'forming with the intermediate shell one or more resonator chambers or cavities, each of which connects with an impedance chamber preferably around the adjacent end of the intermediate shell, and I furthermore provide a neck connecting the impedance chamber with the resonator chamber, the neck being formed between an imperforate portion of the inner conduit and the intermediate shell. The muiier shown on Figs. 2 and 3 includes the usual outer shell I0, the ends of which are secured to end headers or bailies II and I2 which have openings or tubular extensions to which the exhaust pipe B and the tail pipe C are respectively connected, for example, by means of clamps Il and I5. I6 represents an inner shell or conduit which is provided throughout the greater portion of the length thereof with a plurality of perforations or openings I'I. In the particular construction shown, the inner conduit is also provided with integral outwardly bent portions adjacent to the perforatons forming louvers for discharging gases from the inner shell in a tangential direction, but openings of any other kind may be provided in the inner conduit or shell.

I8 represents an intermediate shell spaced between the inner conduit and the outer shell and I9 represents a baie or partition arranged between the intermediate and outer shells to divide the space between these shells into two separate chambers. This partition may be omitted or a plurality of partitions may be employed, if desired. Other partitions 20, 2|, and 22 are arranged between the inner conduit and the intermediate shell to form a plurality of sound impedance chambers 24, 25, 26 and 2T.

` It will be noted that the portion of the inner shell or main conduit adjacent to the ends thereof is unperforated, thus forming between the inner and intermediate shells an annular neck portion 33 through which sound or impulse waves may pass from the impedance chamber 24 to a resonating chamber 28 between the intermediate and outer shells. From the impedance chamber il sound or impulse waves may pass through a neck 34 to another resonator chamber 29. The rear end of the intermediate shell is shown unsupported and is provided with a reinforcing cuff 3d formed by bending the metal of the end of the intermediate shell back against itself. The front end of the intermediate shell is supported from the outer shell by a partition or perforated baille 3 having a series of apertures 32 therein to permit sound from the neck portion 33 to pass through the apertures 32 into the resonating chamber 2t.

In view of the fact that the cross sectional areas of the neck portions 33 and 34 are materially less than those of the chambers 28 and 29, this relation of the neck portions to the chambers results in resonating chambers operating on the principle of the Helmholtz resonator. The perforated partition or baille 3l has been found desirable in that it eliminates certain metallic sounds from the noise of the exhaust. If desired, a similar partitionrcould be used at the other end of the muffler, or in certain cases, it may be possible to omit the partition 3| or to replace the same by other means for eliminating certain metallic-like sounds from the exhaust.

It will be obvious that the formula can be easily applied to the proportioning of the parts of the muiiler to eliminate certain objectionable sounds and from the formula, it will be obvious that by lengthening the neck, which, for example, could be done by providing a longer portion of the inyner conduit without perforations, the frequency of the resonating chamber will be lower. Also the larger the cavity of the resonating chamber the lower its frequency. The sizes of thc resonator cavities or chambers 28 and 29 can, of course, be readily varied by adjusting the baie I9 or by variations in the diameters of the intermediate or outer shells. In applying the formula to any of the mufilers shown in the drawings, the length of the tail pipe must include the length of the adjacent imperforated portion of the inner shell or conduit.

10 The mufilcr shown in Fig. 4 is somewhat similar in construction to that shown in Figs. 2 and 3. In this muffler, the main conduit or inner shell 35 is provided with circular perforations, and the intermediate shell 36 has its ends unsupported.

l5 In this muffler, two baffles 31 are provided between the inner and intermediate shells, thus forming three sound impedance chambers 38, 39 and 4|), the chamber 38 communicating through a neck portion 4| with a resonance chamber or cavity 42 and the sound impedance chamber 40 communicates through a neck 43 with a resonator chamber or cavity 44.

The muiller shown in Figs. 5 and 6 is somewhat similar to those already described, except that in this case the intermediate shell is provided with an outwardly flared end 48 and the opposite end of the intermediate shell is supported on a baille or supporting member 49 secured to an end head or baffle 50 and provided with perforations 5|, this 3" baffle being similar in its action to the baffle 3| described in connection with Figs. 2 and 3.

In the muffler shown in Figs. 5 and 6, a neck portion 52 is provided at one end of the intermediate shell, while at the other end the perforations extend almost to the end of the intermediate shell so that practically no neck is formed between the inner and intermediate shells, but a short neck portion is formed between the outwardly flaring end 48 of the intermediate shell and the end head il or baille 54 of the mufller. It will be obvious that by variation of the length of the neck and the size of the resonating chambers between the intermediate and outer shells, the muffler can be readily tuned in accordance with my formula to eliminate certain wave bands which would produce resonance in the tail pipe.

In Figs. 7 to 9 is shown another slightly modified form of muffler in which only a single baffle or partition 60 is provided between the inner or main conduit 6| and the intermediate shell 62. In this construction, the neck connecting with the impedance chamber 63 is in the form of a plurality of separate ducts or passages. It will be noted that by reference to Figs. 7 and 9, the intermediate shell has a plurality of longitudinal inwardly extending ribs or grooves 65 formed therein, the inner surfaces of which contact with the inner shell or conduit 6|, thus formingamember of elongated separated ducts or necks 66 leading from the sound impedance chamber 63 to the resonator chamber 61. These grooves or depressions in the intermediate shell, in addition to forming a plurality of separated passages also serve to support the outer end of the intermediate shell from 65 the inner shell or conduit. It is not intended, however, to limit this invention to the formation of these depressions or grooves on the intermediate shell, since any other spacing means connecting the conduit and intermediate shell 0 may be employed to divide the neck portion of the resonator chamber into a plurality of neck portions for eliminating from the exhaust certain high frequency metallic-like sounds generated in the muffler. 75 At the discharge end of the muffler, the outer end of the intermediate shell is provide'd with a pair of inwardly pressed portions 68 which are also. arranged to contact with the inner shell, to sup! port this end of the shell from the inner conduit. Between these inwardly pressed portions 68 are formed passages 69 connecting the neck 10 with the resonance chamber 1|. Any other means for supporting the ends of the intermediate shell on parts of the mufiler may be employed, and other means for forming elongated channels or tubes of reduced cross sectional area between the inner and intermediate shells may be employed, if desired. By means of the construction shown in Figs. 7 to 9, the cross sectional area and length of the resonator neck can readily be varied so as to produce a combination of neck and resonance chamber by means of which a definite frequency band of sound can be attenuated.

I claim as my invention: r

1. A muffler comprising an imperforate outer shell, apertured end heads connected to said outer shell, a conduit connecting withI the apertures in said heads to provide a through passage for exhaust gases, said conduit having a portion of its apertures, an intermediate shell continuous from end to end thereof and having both ends spaced from said heads, a partition between said conduit and said intermediate shell and dividing the space between said conduit and intermediate shell into a plurality of inner elongated chambers a partition dividing the space between said intermediate and outer shell into a plurality of outer resonator chambers, the inner chamber at each end of the muffler communicating around the adjacent end of the intermediate shell with a resonating chamber, said conduit being provided with apertures tor cavity.

2. A muffler comprising an imperforate outer shell, apertured end heads connected to said outer shell, a conduit connecting with the apertures in said heads to provide a through passage for exhaust gases, said conduit having a portion of its provided with a plurality of relatively small apertures, an intermediate shell continuous from end to end thereof and having both ends spaced from said heads, a partition between said conduit and said intermediate shell and dividing the space between said conduit and intermediate shell into a plurality of inner elongated chambers, a partition dividing the space between said intermediate and outer shell into a plurality of outer resonator chambers, the inner chamber at each end of the mufller communicating around the adjacent end of the intermediate shell with a resonating chamber, said conduit being provided with apertures opening into each inner chamber, and a tail pipe which has fundamental resonance frequencies in harmonic relation to those of the resonator chambers within said muffler.

3. A muffler comprising an imperforate outer shell, apertured end heads connected to said outer shell, a conduit connecting with the apertures in said heads to provide a through passage for exhaust gases, said conduit having a, portion of its length provided with a plurality of relatively small apertures, an intermediate shell having both ends thereof spaced from said heads, a partition between said conduit and said intermediate shell and dividing the space between said conduit and intermediate'shell into a plurality of inner elongated chambers, a partition dividing the space between said intermediate and outer shell into a plurality of outer resonator chambers, the inner chamber at each end of the muiller communicating around the adjacent end of the intermediate shell with a resonating chamber. said conduit being provided with apertures opening into each inner chamber and being provided with imperforate portions near the ends oi said conduit forming with the intermediate shell resonator necks connecting with said resonator cavities, and a tail pipe which has fundamental resonance frequencies in harmonic relation to those of the resonator chambers within said muffler.

4. A mufiler including a tail pipe, and a sound and gas conducting conduit extending through said muffler and having a portion thereof provided with perforations, resonator chambers each coupled acoustically with said conduit through said perforations by means of a neck portion of less cross sectional area than the cross lsectional area of the resonator chamber and having fundamental resonance 'frequencies corresponding to the natural fundamental frequencies or harmonies of said tail pipe.

5. A muiller for use in connection with silencing the exhaust from an internal combustion engine and having a tail pipe, a main conduit through which the gases pass, an intermediate shell partly surrounding said main conduit and open at an end, and an outer conduit arranged about the intermediate conduit and forming with the same a resonator chamber, said conduit being provided at intervals with perforations through which gases and sound waves may pass from said conduit into the space between said conduit and said intermediate shell, an end part of said intermediate shell forming with an unperforated portion of said conduit a resonator neck, the parts of the muiiier being proportioned in accordance with the following formula:

in which N=frequency to be attenuated =area of perforation in conduit communicating with the neck divided by the cross sectional area of the conduit, the former area not exceeding the latter area;

c=velocity of sound in the medium;

s: cross-sectional area of resonator neck, which should be approximately equal to the cross sectional area of the conduit;

L=1ength of resonator neck amasar 6. A mumer for use in connection with silencing the exhaust from an internal combustion engine and having a tall pipe, a main conduit through which the gases pass, an intermediate shell partly surrounding said main conduit and open at an end, and an outer conduit arranged about the intermediate conduit and 4forming with the same a resonator chamber, said conduit being provided at intervals with periorations through which gases and sound waves may pass from said conduit into the space between said conduit and said intermediate shell, an end part of said intermediate shell forming with an unperforated portion of said conduit a resonator neck, the parts of the muffler being proportioned in accordance with the following formula:-

in which: N :frequency to be attenuated =area of perforation in conduit communicating with the neck. divided by the cross sectional area of the conduit, the former area not exceeding the latter area; c=velocity of sound in the medium R=radius oi a circle of equal crosssectional area as the neck which cross sectional area should be approximately equal to the cross sectional area of the conduit L=length of neck L1=1ength of cavity R1=radius of a circle of equal crosssectional area as the cavity,

7. A muilier having a sound and gas conduit extending therethrough, intermediate and outer shells arranged about said conduit, end heads connected with said outer shell and having apertures in alinement with said conduit and spaced beyond the ends of said intermediate shell, said conduit having a perforated portion of less length than said intermediate shell and terminating at distances from the ends of said intermediate shell, and an annular supporting member secured to an end of said intermediate shell and extending outwardly from said intermediate shell and having its outer part secured to another part of said muiiler for supporting said end of said intermediate shell and having apertures through which gases and sound waves may pass from the space between said conduit and intermediate shell to the space between said intermediate and outer shells, the combined area of the apertures in said supporting member being approximately equal to the cross sectional area. of the space between said conduit and the intermediate shell. 

